Order Model
Recently Published Documents


TOTAL DOCUMENTS

2887
(FIVE YEARS 1340)

H-INDEX

60
(FIVE YEARS 24)

2021 ◽  
Vol 11 (12) ◽  
pp. 5650
Author(s):  
Jose Joaquin Sánchez-Álvarez ◽  
Carlos Martel

Intentional mistuning is a common procedure to decrease the uncontrolled vibration amplification effects of the (unavoidable) random mistuning, and to reduce the sensitivity to it. The idea is to introduce an intentional mistuning pattern that is small, but much larger than the existing random mistuning. The frequency of adjacent blades is moved apart by the intentional mistuning, reducing the blade-to-blade coupling and, thus, the effect of the random mistuning. In order to clearly show the action mechanisms of intentional mistuning, we focus in this work in a quite simple configuration: forced response of a blade dominated modal family in a mistuned rotor with linear material damping. The problem is analysed using the asymptotic mistuning model methodology. A more reduced order model is derived that allows us to understand the relevant parameters behind the effect of intentional mistuning, and gives a simple expression for the estimation of its beneficial effect. The results from the reduced model are checked against detailed FEM simulations of two mistuned rotors.


2021 ◽  
Author(s):  
Sidra Shaoor Kiani ◽  
Atif Ullah ◽  
Amjad Farooq ◽  
Masroor Ahmad ◽  
Naseem Irfan ◽  
...  

Abstract In order to provide protection against extremely toxic gases Activated Carbon (AC) adsorption has long been regarded to be a useful technology in terms of gas removal. AC without chemical impregnation has been considerably less effective than impregnated ACs. AC in present use was modified with an organic amine i.e. triethylenediamine (TEDA) to enhance the physical and chemical properties of AC in order to remove specific poisonous gases. Purpose of this study was to assess the TEDA impregnated AC in terms of adsorption capability for simulant gas like SO2. Analysis was done in a properly designed setup. By using the scheme reported here, significant adsorption of toxic gas was obtained. Maximum removal capability observed by AC-4 for SO2 gas was 3.74 g/g-C and its breakthrough time was 264 minutes. Breakthrough time and adsorption capacity of AC-4 was found to be 25 times and 10 times greater as compared to raw AC. Different characterization techniques were also used to study impregnated AC. It was found that chemical adsorption was the crucial means by which TEDA impregnated AC removed the simulant gas. Langmuir model was best to represent equilibrium and adsorption kinetics follow second order model. The process was endothermic, favorable and spontaneous.


2021 ◽  
Author(s):  
Ibrahim Touzani ◽  
Kawtar FIKRI-BENBRAHIM ◽  
Hammou Ahlafi ◽  
Bouchaib Ihssane ◽  
Otmane Boudouch

Abstract Ziziphus lotus (Nbeg) is very common in Morocco where it occupies various ecosystems and presents different interests; however it remains devalued and knows recent deterioration due to the human pressure through clearing, wood collection, irrational cuts’ exploitation and overgrazing. This study aims to prepare activated carbon from the cores of this interesting biomaterial, for the first time to the best of our knowledge, according to a manufacturing process based on its chemical and thermal activation. The cores of Ziziphus lotus (Nbeg) were chemically activated by sulfuric acid (H2SO4, 98%) for 24h with a mass contribution (1:1), and then carbonized at a temperature of 500 °C for 2 hours. The obtained activated carbon was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and specific surface measurement. These characterization results showed an important porosity and a surface structure having acid groups and carboxylic functions. The adsorption of methylene blue (MB) was evaluated, by Langmuir and Freundlich models examination, in order to explain the adsorption efficiency in a systematic and scientific way. Also pseudo-first order and pseudo-second order kinetic models were used to identify the possible mechanisms of this adsorption process. The results showed that the MB adsorption process on activated carbon follows the Langmuir model and that the adsorption kinetic is best represented by kinetics data of the pseudo-second order model. Therefore, Z. lotus can be used as a low-cost available material to prepare a high quality activated carbon having a promising potential in the wastewater treatment.


2021 ◽  
Vol 118 (25) ◽  
pp. e2025236118
Author(s):  
Romain Enjalbert ◽  
David Hardman ◽  
Timm Krüger ◽  
Miguel O. Bernabeu

The tumor microenvironment is abnormal and associated with tumor tissue hypoxia, immunosuppression, and poor response to treatment. One important abnormality present in tumors is vessel compression. Vessel decompression has been shown to increase survival rates in animal models via enhanced and more homogeneous oxygenation. However, our knowledge of the biophysical mechanisms linking tumor decompression to improved tumor oxygenation is limited. In this study, we propose a computational model to investigate the impact of vessel compression on red blood cell (RBC) dynamics in tumor vascular networks. Our results demonstrate that vessel compression can alter RBC partitioning at bifurcations in a hematocrit-dependent and flow rate–independent manner. We identify RBC focusing due to cross-streamline migration as the mechanism responsible and characterize the spatiotemporal recovery dynamics controlling downstream partitioning. Based on this knowledge, we formulate a reduced-order model that will help future research to elucidate how these effects propagate at a whole vascular network level. These findings contribute to the mechanistic understanding of hemodilution in tumor vascular networks and oxygen homogenization following pharmacological solid tumor decompression.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
James F. Amaku ◽  
Segun Ogundare ◽  
Kovo G. Akpomie ◽  
Collins U. Ibeji ◽  
Jeanet Conradie

AbstractMultiwalled carbon nanotubes/quartzite nanocomposite modified with the extract of Dacryodes edulis leaves was synthesized and designated as Q, which was applied for the removal of Cr(VI) from water. The adsorbents (PQ and Q) were characterized using the SEM, EDX, FTIR, TGA, XRD, and BET analyses. The XRD revealed the crystalline composition of the nanocomposite while the TGA indicated the incorporated extract as the primary component that degraded with an increase in temperature. The implication of the modifier was noticed to enhance the adsorption capacity of Q for Cr(VI) by the introduction of chemical functional groups. Optimum Cr(VI) removal was noticed at a pH of 2.0, adsorbent dose (50 mg), initial concentration (100 mg dm−3), and contact time (180 min). The kinetic adsorption data for both adsorbents was noticed to fit well to the pseudo-second-order model. The adsorption equilibrium data were best described by the Langmuir model. The uptake of Cr(VI) onto PQ and Q was feasible, endothermic (ΔH: PQ = 1.194 kJ mol−1 and Q = 34.64 kJ mol−1) and entropy-driven (ΔS : PQ = 64.89 J K−1 mol−1 and q = 189.7 J K−1 mol−1). Hence, the nanocomposite demonstrated potential for robust capacity to trap Cr(VI) from aqueous solution.


2021 ◽  
Author(s):  
Ram Kumar ◽  
Afzal Sikander

Abstract The Coulomb and Franklin laws (CFL) algorithm is used to construct a lower order model of higher-order continuous time linear time-invariant (LTI) systems in this study. CFL is quite easy to implement in obtaining reduced order model of large scale system in control engineering problem as it employs the combined effect of Coulomb’s and Franklin’s laws to find the best values in search space. The unknown coefficients are obtained using the CFLA methodology, which minimises the integral square error (ISE) between the original and proposed ROMs. To achieve the reduced order model, five practical systems of different orders are considered. Finally, multiple performance indicators such as the ISE, integral of absolute error (IAE), and integral of time multiplied by absolute error were calculated to determine the efficacy of the proposed methodology. The simulation results were compared to previously published well-known research.


Author(s):  
Luiz F. O. Maia ◽  
Guilherme Lages ◽  
Patricia C. C. Ladeira ◽  
Bruno Lemos Batista ◽  
Márcia C. S. Faria ◽  
...  

Abstract δ-FeOOH, a magnetic iron oxyhydroxide, has a significant number of -OH groups on its surface. These provide an attractive platform for heavy metal species in contaminated water, giving it potential as an adsorbent. Its performance can be improved by increasing the number of active surface sites. δ-FeOOH hollow structures were synthesized on a mesoporous silica surface then treated with NaOH solution. X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed that structure synthesis was successful. δ-FeOOH, 5,27 nm, hollow crystals were produced with 63 m2 g−1 surface area and 20 nm average pore size. The point of zero charge was 4.72, which is beneficial for Hg(II) adsorption near neutral pH. The maximum Hg(II) adsorption capacity at pH 7 was determined as 89.1 mg g−1. The kinetics data were best fitted by a pseudo-second-order model with k2 equal 0,1151 g mg−1min−1. Finally, a nanomaterial filter was developed and used to remove mercury in water samples from a Brazilian river.


Axioms ◽  
2021 ◽  
Vol 10 (2) ◽  
pp. 122
Author(s):  
Maryamsadat Hedayati ◽  
Reza Ezzati ◽  
Samad Noeiaghdam

Coronaviruses are a group of RNA (ribonucleic acid) viruses with the capacity for rapid mutation and recombination. Coronaviruses are known to cause respiratory or intestinal infections in humans and animals. In this paper, a biologically compatible set of nonlinear fractional differential equations governing the outbreak of the novel coronavirus is suggested based on a model previously proposed in the literature. Then, this set is numerically solved utilizing two new methods employing sine–cosine and Bernoulli wavelets and their operational matrices. Moreover, the convergence of the solution is experimentally studied. Furthermore, the accuracy of the solution is proved via comparing the results with those obtained in previous research for the primary model. Furthermore, the computational costs are compared by measuring the CPU running time. Finally, the effects of the fractional orders on the outbreak of the COVID-19 are investigated.


2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zheng Liu ◽  
Yuling Wei

Activated carbons (ACs) were prepared from pomelo peels by K2CO3 activation and used as an adsorbent (PAC) for the removal of Cu(II) from aqueous solutions. BET, SEM, and FT-IR were employed for the characterization of the obtained ACs. The optimum ACs were reported at activation temperature of 850°C, activation time of 60 min, and impregnation ratio of 3, which had a high surface area (1213 m2/g) and total pore volume (0.57 cm3/g). The resulting ACs were used for the adsorption of Cu(II) from aqueous solutions in the batch mode and yielded a superior adsorption capacity of 139.08 mg/g. The pH of optimum adsorption was determined as 5. Pseudo first-order model, pseudo second-order model, and intraparticle diffusion model were applied to describe the adsorption processes. The adsorption kinetic data were found to follow the pseudo second-order model. The adsorption isotherms data were analyzed using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich models. The Langmuir model was found to provide the best fit, and the calculated adsorption capacity was 151.35 mg/g.


Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3277
Author(s):  
Wenjuan Zhu ◽  
Zhiyong Yang ◽  
Akram Yasin ◽  
Yanxia Liu ◽  
Letao Zhang

The poly (acrylic acid-acrylamide/starch) composite was synthesized by solution polymerization, aiming to adsorb mercury (II) in water. The resulted copolymer was characterized by particle size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), scanning electron microscopy (SEM) and dynamic light scattering particle size analyzer (DLS). It turned out that starch was successfully incorporated with the macromolecular polymer matrix and played a key role for improving the performance of the composites. These characterization results showed that the graft copolymer exhibited narrow molecular weight distribution, rough but uniform morphology, good thermal stability and narrow particle size distribution. The graft copolymer was used to remove Hg(II) ions from aqueous solution. The effects of contact time, pH value, initial mercury (II) concentration and temperature on the adsorption capacity of Hg(II) ions were researched. It was found that after 120 min of interaction, poly (acrylic acid-acrylamide/starch) composite achieved the maximum adsorption capacity of 19.23 mg·g−1 to Hg(II) ions with initial concentration of 15 mg·L−1, pH of 5.5 at 45 °C. Compared with other studies with the same purpose, the composites synthesized in this study present high adsorption properties for Hg(II) ion in dilute solution. The adsorption kinetics of Hg(II) on the poly (acrylic acid-acrylamide/starch) composite fits well with the pseudo second order model.


Export Citation Format

Share Document